The present invention relates to systems and methods for determining the presence of objects within a body of water. In particular, the present invention relates to a system and method for detecting the presence of objects within a body of water covered by a body of ice.
Depth finding transducer systems are in widespread use to detect the presence of fish or other objects within a body of water. For example, a fisherman in a boat on open water can use a depth finding transducer system to detect both the depth of the water below the boat and the presence or absence of any fish or other objects below the boat.
A typical conventional depth finding system used on a boat includes a base display unit, a transducer, and a cable for connecting the transducer to the display unit. The transducer produces a sonar wave that is projected into the body of water in the shape of a cone for detecting the presence of objects within the water. In most cases, the transducer is rotatably or pivotally mounted to a hull of a boat in a location at which the transducer is at least partially submerged within the body of water. For example, the transducer can be mounted either on a side of the boat or at the rear of the boat. This rotatable mounting permits the transducer to be manipulated to insure the desired orientation of the sensing cone projected into the water.
Depth finding transducer systems are also used in situations in which a fisherman is not located in a boat on an open body of water. Instead, the fisherman may be located on shore but desires to detect the presence of objects such as fish within the body of water at a distance from the shore. Altmire et al. U.S. Pat. No. 4,995,009 provides one example of a castable fish/depth finder which permits a fisherman to "cast out" a depth finding transducer a spaced distance from the shoreline for determining the presence of objects below the transducer within a body of water.
Depth finding transducer systems can also be used in ice fishing to detect the presence of objects such as fish within a body of water below a body of ice covering the water. A prior art depth locator typically used in ice fishing is shown in FIG. 1. As shown in FIG. 1, a body of water 10 is covered by a body of ice 12. A bottom land surface 14 defines a lower boundary of the body of water 10 while the body of ice 12 defines the upper boundary of the body of water 10. The body of ice 12 can also include a hole 16 formed therein to provide access to the body of water 10. A fishing rod 18 is positioned adjacent the hole 16 to permit a fishing line 20 to extend through the hole 16 in the body of ice 12. A bait/hook combination 22 is provided at an end of line 20 and is located within the body of water 10, preferably adjacent a fish 24.
As shown in FIG. 1, a prior art depth finder system 29 typically includes a display unit 30, a transducer 32, and a positioning cable 34. The transducer 32 is capable of transmitting a sonar wave through the body of water 10 in the shape of a sensing cone 36A for detecting the presence of objects (e.g., fish 24 or bait/hook 22) within the cone 36A, as well as for determining the depth of the body of water 10. The positioning cable 34 provides an electrical and mechanical connection between the transducer 32 and the display unit 30. The positioning cable 34 is flexible yet capable of holding a desired shape or configuration created by manual manipulation of the shape of the cable 34. The transducer 32 is typically side mounted adjacent an end of the positioning cable 34. The display unit 30 includes electronic circuitry, a display, and a power source. The display unit 30 is typically mounted on or rests on a top surface of the body of ice 12 while the positioning cable 34 can be extended through the hole 16 in the body of ice 12 to position the transducer 32 within the water 10 to produce the sensing cone 36A within the water 10.
When placing the transducer 32 below the surface of the body of ice 12, it is desirable that a bottom surface of the transducer 32 be substantially planar with respect to a horizontal plane such as the bottom land surface 14. This orientation can be accomplished by aligning a longitudinal axis of the transducer 32 substantially perpendicular to the land surface 14. This desired orientation of the transducer 32 will produce a sonar wave oriented like sensing cone 36B (shown in FIG. 1), which is projected within the body of water 10 so that the bait 22 sits substantially within a center of the sensing cone 36B where the transducer sensitivity for detecting objects (e.g., fish) is the greatest. Fishermen attempt to achieve desired positioning of transducer 32 to yield sensing cone 36B by maneuvering the shape holding positioning cable 34. Unfortunately, actually achieving the desired orientation of transducer 34 to produce an optimally positioned sensing cone (like sensing cone 36B) is difficult due to the shape holding characteristics of the positioning cable 34. For example, the positioning cable 34 may have kinks or bends 35, as shown in FIG. 1, which are produced during maneuvering of the cable 34. These bends 35 interfere with a fisherman's attempts to align the cable 34 and transducer 32 in the desired orientation.
Frequently, the sensing cone 36A is produced despite a fisherman's best efforts at achieving sensing cone 36B. As seen in FIG. 1, when transducer 32 is oriented to project sensing cone 36A, the bait 22 sits at the edge of sensing cone 36A where the transducer sensitivity for detecting objects (e.g, fish) is the lowest. A fisherman compensates for orientation of sensing cone 36A by increasing the gain of the display unit until the bait/hook 22 can be clearly monitored on the display unit. However, increasing the gain usually reduces the sensitivity of the display unit to detecting fish not immediately adjacent the bait/hook combination, thereby artificially limiting the zone about the bait/hook 22 in which fish can be detected. This arrangement makes it more difficult to detect the presence of fish 24 adjacent the bait 22.
Currently, there are two methods for dealing with this transducer orientation problem. First, a bubble level (not shown) can be placed on the top of the transducer 32 which allows the fisherman to determine whether a bottom surface of the transducer 32 is oriented in the proper plane. In this method, the transducer 32 is preferably placed near a surface 37 of the body of water 10 so that the position of the transducer 32 can be easily manipulated in conjunction with the bubble level to achieve the proper leveling effect. However, transducers 32 placed near the surface of the water 10 produce a lot of "noise" reported on the display unit 30. This noise is generally undesirable and disliked by fishermen. Accordingly, this technique is not frequently used.
Alternatively, in an effort to avoid unnecessarily increasing the gain of the display unit, the fisherman may manipulate the positioning cable 34 and transducer 32 until the position of the transducer 32 corresponds to the strongest bait signal reported on the display base unit 30. In this situation, the fisherman presumes that the transducer 32 is level when the display unit 30 reports the strongest object identification signal, since the bait 22 should be hanging straight down in the water 10. However, this method can require extensive adjustment of the positioning cable 34 before a satisfactory alignment of the transducer 32 is achieved. Moreover, if a fisherman catches a fish, the transducer 32 and cable 34 are typically removed from the hole 16 before the fisherman lands the fish. This also necessarily requires either disconnecting the positioning cable 34 from the display unit 30 or moving the display unit 30 along with the positioning cable 34 and transducer 32. In either case, the transducer 32 must be repositioned once the depth finder system is re-employed within the hole 16 and body of water 10. Fishermen would like to avoid repositioning a depth finder system when ice fishing.